We have around 200g of dry picric acid in our lab, used to view grain structures in martensitic steels.

Our picric is used infrequently (once every 1--2 years) as it's for a very specific test. It is stored in a plastic bottle and I assume it's pre 2015 as it doesn't have the current GHS hazard symbols. I'm happy that we have effective control measures for the general health hazards, however. I've read up on the explosive properties of dry picric, but would appreciate some adivce on the reality of this. How explosive is it? How susceptible to impact/shock is it actually? Does it have a general expiry date (none listed on the bottle) as I understand it becomes more unstable as crystals form over time.

Ideally we'd dispose of it (appropriately) but our senior technician is adamant that we need to hold onto it for ttesting. Essentially, if anyone can make me less ignorant to the dangers of dry picric so I can make an informed decision, I'd really apppreciate it!

Picric acid, a mysterious substance that appears in the back of lab cupboards and creates waves of panic. It is also known as known as 2, 4, 6-trinitrophenol (TNP) and it classed as an explosive under the UN labelling scheme.

The first thing to note is that if it is allowed to dry out it becomes a serious explosive and this is what people who only use it  occasionally come across. Even worse, is the fact that it can form metal compounds that are very unstable. These form under the metal lid/cap and the energy from turning this cap can be enough to set off the explosive.

As it is an explosive under the UN labelling scheme it is classed as such under the Explosives Regulations 2014, which means that if you wish to keep it, you require an explosives certificate. If it is whetted it becomes a desensitised explosive but under the regs this still needs a  certificate unless it is a solution that is less than 2% picric acid.

If you need to use more concentrated picric acid you need to obtain a certificate.

There are legal exceptions for quantities not exceeding 5 grams, for:

1. Research, analysis or testing at a University;
2. Research, analysis or testing by or on behalf of the Crown; or
3. The application of forensic science by or on behalf of a police force or the Crown.

Otherwise you will need the certificate

I have been lucky since where I have worked , the Civil Service we were subject to Crown Immunity and we used it to stain the  wings of  seagulls(don’t ask)!  

Disposal can be tricky. There are companies who will if it is suitably whetted can and will dispose of it. I know of several educational establishments who called in the bomb squad and had them get rid of their stock of picric acid by detonating in some remote location!

Edited by user 29 November 2019 10:49:03(UTC)  | Reason: missing words

In my fire service days I was in charge of an incident where picric acid had dried out and hospital staff had telephoned the Brigade to ask for advice. Of course a full hazmat incident was created 

The embarrassed lab manager showed me a plastic outer spill container with a glass jar inside. The guy said it should be a liquid, but then shook the plastic container and it sounded like coffee granules. However, all I was focused on and more than a little nervous of was the explosive label on the face of the outer container.

I asked him to put it down gently and leave the room. I telephoned our scientific advisor who said not to touch the jar as it was now shock sensitive. Any heat may cause an explosion. We shouldnt even unscrew the lid as any granules in the thread now heated by unscrewing the lid may take a hand off

He advised evacuating the building. I told him there were two surgical operations taking place in the next room behind a double skin brick wall. His advice was the same. Stop the operations and evacuate 

Then a game of cat and mouse. The local authority said they had no capability to dispose of this stuff and the bomb squad should do it. The Met Police bomb squad said nuffin to do with us Guvnor - try the local authority

Eventually the Police did remove the container from the hospital 

So be very very careful of dried picric acid. My understanding is that many schools and colleges dont hold it now and its rarely used, mainly due to licensing issues. You can see why!!

If you're still in need of some assistance/advice, we have experience in re-hydrating dry picric acid in-situ before removing it for safe disposal.